The main techniques and approaches of biochemical cytology, resting largely on the combined use of cell fractionation, biochemical analysis and electron microscopy are applied to the study of the protozoan, Trichomonas vaginalis, the causative agent of a venereal disease, trichomoniasis. In this mitochondria-free organism we will study the enzyme mechanisms and compartmentalization of the anaerobic and aerobic metabolism, with special attention to the microbody-like hydrogenosomes. The effect of metabolic inhibitors and of antitrichomonad drugs on the metabolism will be investigated. The hydrolases and the lysosomal system of the organism will be characterized. Special attention will be given to the differences of this system in different physiological conditions and in strains with different level of pathogenicity.